Petrogenesis of the granitic porphyry related to the giant molybdenum deposit in Donggou, Henan province, China: Constraints from petrogeochemistry, zircon U-Pb chronology and Sr-Nd-Hf isotopes

In this study, we carried out a comprehensive research including zircon U-Pb dating, petrogeochemistry and Sr-Nd-Hf isotope analysis on the granitic porphyry related, to the giant molybdenum deposit in Donggou, Henan Province, China. LA-ICP-MS zircon U-Pb chronology indicated that the Donggou porphyry emplaced at 114 - 117Ma, identical with the time when the molybdenum deposit were formed (116 ±2Ma, Re-Os age). Both the Donggou porphyry and the large Taishanmiao batholith to its south are enriched in Si, K, LILEs such as Rb, Th and U, and HFSEs such as Nb, Ta, Zr and Hf, while depleted in Fe, Mg, Ca, Sr and Ba. They are weakly peraluminous and show high Ga/AI ratios, and thus can be classified as aluminous A-type granite. The primitive magma experienced very high extent of crystal, fractionation and then, emplaced to form the Donggou porphyry in an extension setting. The Nd isotopic compositions of the Donggou samples range from 0. 51166 to 0. 51182, with corresponding ε_Nd (t) values of - 17. 3 to -14.3. The ε_Hf(t) values also show a large range (-3.4 to -18.7) with a xenocryst yielding e _Hf(t) value of -2. 4 at 1715Ma. Based, on above isotopic data, we argue that the magma sources of the Donggou porphyry were composed of mainly old crustal rocks, but may also involve some portions of mantle materials. We suggested that input of mantle-derived melt and highly evolved nature of the Donggou porphyry are important for the formation of the giant molybdenum deposit.